The investigators broad objective is to develop methods for priming strong CTL and CD4 T cell responses to HIV using protein-based vaccines. The rationale for this focus is that these multiple immune responses should give the strongest protection. However, protein immunogens, which are desirable because they are in principle safer than live vaccines, fail to stimulate CTL immunity which may be one of the most important responses against HIV. Moreover, without strong adjuvants (which cannot be used in man) protein immunogens often elicit only weak and short-lived CD4-dependent immunity. In the previous funding period the investigators hypothesized that a novel antigen presenting pathway could be exploited to elicit CTL responses with protein immunogens. Their experimental approach was successful. In the present renewal, they will further develop this approach. They have 3 specific Aims: Aim 1: Develop methods to prime CTL immunity with non-living (protein) immunogens. The first objective of this Aim is to use our existing technology to develop a subunit vaccine with HIV antigens that elicits CTL immunity. The second objective is to further develop this technology so that it elicits the strongest possible immune response. The hypothesis underlying this second objective is that stronger antigen presentation will result in greater and longer lasting immunity. One experimental approach will increase antigenicity through modifications that enhance in antigen presenting cells that uptake of antigen and the rate of antigen processing. Another approach will attempt to increase immunogenicity through the formulation of antigen constructs with cytokines. Aim 2: Develop methods to prime concomitant MHC class I and II-restricted responses and mucosal immunity with protein immunogens. The hypothesis underlying this Aim is that optimal anti-viral vaccines will need to elicit not only CTL responses but also CD4 T cell responses and both systemic and mucosal immunity. The goal of this Aim is to engineer their antigen preparations from Aim 1 so that they elicit MHC class II- restricted responses (particularly Th1) and mucosal immunity. Important objectives will be oral bioavailability and systemic formulations that do not require inflammatory adjuvants. Aim 3: Evaluate vaccine strategies in primates. The goal of this Aim is to evaluate and adapt their methodologies for eliciting CTL and class II-restricted immunity in primates. Their experimental approach is to develop methodology to assay the activity of our antigen constructs in primate APCs. Once they identify active formulations and optimize their potency for primate cells, they will test their ability to elicit immune response in vivo in non-human primates.